Twelve Nights in Hollywood is a new box set of Ella Fitzgerald performing over a twelve day period in a small jazz club in Los Angeles. Remarkably, none of the tracks have been released before, despite a scarcity of live recordings in small venues, and despite the quality of the performances.

Gary Giddins, the veteran critic and author of “Jazz,” agrees. “This ranks on the top shelf of her live recordings,” he said. “It’s about as good as it gets.”

Why these tapes stayed locked in the vault for nearly half a century — and what it took to set them free — is a tale of a producer’s neglect, a jazz sleuth’s obsession and a string of happy coincidences.